/*
 * Copyright 2015 GenerallyCloud.com
 *  
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *  
 *      http://www.apache.org/licenses/LICENSE-2.0
 *  
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */ 
package com.generallycloud.nio.codec.fixedlength;

import java.io.IOException;

import com.generallycloud.nio.buffer.ByteBuf;
import com.generallycloud.nio.codec.fixedlength.future.FixedLengthReadFutureImpl;
import com.generallycloud.nio.component.SocketSession;
import com.generallycloud.nio.protocol.ChannelReadFuture;
import com.generallycloud.nio.protocol.ProtocolDecoder;

/**
 * <pre>
 *  B0 - B3：
 *  +-----------------+-----------------+-----------------+-----------------+
 *  |        B0                B1                B2               B3        |
 *  + - - - - - - - - + - - - - - - - - + - - - - - - - - + - - - - - - - - +
 *  | 0 1 2 3 4 5 6 7   0 1 2 3 4 5 6 7   0 1 2 3 4 5 6 7   0 1 2 3 4 5 6 7 |
 *  | - - - - - - - - + - - - - - - - - + - - - - - - - - + - - - - - - - - +
 *  |                                                                       |
 *  |                          Data-length(P0-P31)                          |
 *  |                                                                       |
 *  |                                                                       |
 *  +-----------------+-----------------+-----------------+-----------------+
 *  
 *  Data-length:-1表示心跳PING,-2表示心跳PONG,正数为报文长度
 *  注意: 无论是否是心跳报文，报文头长度固定为4个字节
 * 
 * </pre>
 */
public class FixedLengthProtocolDecoder implements ProtocolDecoder {

	public static final int	PROTOCOL_HEADER	= 4;

	public static final int	PROTOCOL_PING		= -1;

	public static final int	PROTOCOL_PONG		= -2;

	private int			limit;

	public FixedLengthProtocolDecoder(int limit) {
		this.limit = limit;
	}

	@Override
	public ChannelReadFuture decode(SocketSession session, ByteBuf buffer) throws IOException {

		return new FixedLengthReadFutureImpl(session, session.getByteBufAllocator().allocate(PROTOCOL_HEADER), limit);
	}

}
